No abstract

We explore the utilization of aromatic diselenides as new low temperature exchangeable monomers for their utilization in thermosets.

In this work, a complete study of the effect of different organocatalysts on the step-growth polyaddition of a 5-membered dicyclic carbonate, namely, diglycerol dicarbonate with a poly(ethylene glycol)-based diamine in bulk at 120 °C was first carried out. The reaction was found to be dramatically catalyst dependent, higher rates being observed in presence of strong bases, such as phosphazenes (t-Bu-P4 or P4) and 5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). Unexpectedly, the as-formed urethane linkages entirely vanished with time, as evidenced by FTIR and 13 C NMR spectroscopies, while signals due to urea bond formation progressively appeared. Advantage of the chemical transformation occurring from urethane to urea linkages was further taken, by optimizing the polymerization conditions to access a range of poly(hydroxyurea-urethane)s (PHUUs) with precise urethane to urea ratio in a one pot process. Characterization of corresponding polymers by rheological measurements showed that the storage modulus reached a plateau at high temperatures and at high urea contents. The application temperature range of poly(hydroxyurea-urethane)s could thus be increased from 30 °C to 140 °C, as for regular polyurethanes. Furthermore, SAXS and phase-contrast microscopy images demonstrated that increasing the urea content improved the phase separation between soft and hard segments of these PHUUs. Altogether, this novel, straightforward, efficient and environmentally-friendly strategy enables the access to non-isocyanate poly(urea-urethane)s with tunable urethane to urea ratio from 5-membered dicyclic carbonates following an organocatalytic pathway.

Polyurethanes are one of the most versatile families of polymers and the largest produced thermoset beyond phenolic resins, epoxies and unsaturated polyesters. Due to their static cross-linked structure, their ability...